Neck pain as a result of chronic cervical spine injury is one of the most common musculoskeletal complaints, especially for an aging workforce where neck pain can become a significant occupational issue leading to lost work time and productivity. As the average age of retirement increases it becomes important to modify the design of appropriate protective equipment and activities for older individuals, but more information is needed about the biomechanics of these activities to properly engineer solutions. Currently, there is no method to assess cervical spine kinematics in real time for human subjects in the course of their workplace and other activities and interests. While CT and MRI are considered the best imaging modalities to evaluate the pathoanatomy contributing to neck pain, excessive size and power requirements limit the ability of these technologies to assess cervical spine kinematics and intervertebral disc displacements in real time for human subjects. We propose to develop a stereographic ultrasound system that can provide portable, robust, dynamic, real-time imaging of the cervical spine in an active aging population to determine the biomechanics of occupational activities and to measure the rigid body kinematics of contiguous vertebrae and intervertebral disc displacements. The alignment and co-registration of images from dual ultrasound transducers, combined with an assumption of rigid body motion will be used to calculate the motion of contiguous cervical vertebrae. Initially we will validate the accuracy and reliability of the rigid body motion data and intervertebral disc displacements measured by the stereographic ultrasound system using isolated human cadaver cervical spine segments mounted in a servo-hydraulic, multi-axial testing machine subjected to representative dynamic forces and moments. This will be followed by testing intact human cadavers subjected to dynamic flexion/extension, lateral tilt and axial rotation moments applied to the head and neck. The rigid body motion data and intervertebral disc displacements measured using ultrasound will be compared to the same data measured using plane radiography. In-vivo cervical spine kinematics and intervertebral disc displacements measured using stereographic ultrasound and dynamic MRI will be compared in human volunteers as they flex/extend, rotate and tilt their head and neck. Finally in-vivo stereographic ultrasound data will be acquired in healthy volunteers subjected to simulated inertial loads typically encountered during the occupational activities of an active aging population to establish the ability of ultrasound to evaluate the biomechanical mechanisms contributing to cervical spine injury and chronic neck pain. .